Sound Deadening, A little more technical question Options

[r_towle]

Hi,
I have been reading lots on the Internet, and the more I read, the more I find that no-one has done any real analysis.

What type of sound does a motor make?
Is it vibration, or soundwaves?

I guess what I am looking for is not the Use Dynamat, Use Brown Bread type of answer.

What if I combined both the ceramic spray on products, and the peal and stick products?
Aside from throwing alot of money at the problem, am I really stopping any more sound waves from coming through?

Are there any discussions of what sound waves Dynamat stops, and what sound waves a spray on ceramic sound deadening system stops?
Are they the same waves?

It seems to me that when you use two of the correct products, each designed to stop a certain type of sound wave, you will get a much better result.

But, where is the info telling me which sound wave is stopped by what product?

Rich

[Katmanken]

In another life I used to quiet down printers- noisy dot matrix printers. Spent many hours in a soundroom with a meter trying to see what worked.

You can get two types of sound to block. One is broadcast sound from a radiant source (motor) and another is from a sympathetic vibration- such as a large vibrating panel. To dampen the panel vibrations, a sheet sandwich of tar and foam and paper mats were used by the factory on the floors, and a sheet of rubber on the bulkhead inner wall. For radiant sound, dense soundfoam works best, and no, it doesn't have to be eggcrate.

Foam absorbs sound and convers it to heat. It was amazing what a well placed sheet of .50 inch to 1.50 inch thick layer of Soundcoat foam would do. Opposed sheets stop richocheting sound, and having one of the opposed pair at an angle is best. Foam for midrange, myar cover on foam for high frequency vibrations.

A really good way to dampen sound is to allow the sound to vibrate a mass. The mass is suspended on a spring (foam sheet or dampening sheet)) and the sound energy vibrates the mass, and the spring or (dampener material converts the vibration to heat and dampens the noise. I have used steel strips on gel or foam or vinyl as a dampener. Soundcoat used to sell a sheet of foam with a vinyl coated lead layer on top of the foam and a sheet of foam on top of that, and a layer of silver mylar on the very top. That stuff was awesome for sound deading but weighed a ton and was spendy. Ever wonder why the engine sound deading on the bulkheadwas a layer of asphalt paper on top of a layer of brown mat? The asphalt paper was the mass, the brown mat was the spring- until the glue crapped out.

Ken